Just like forests on land, underwater kelp forests are sensitive to invasive species from other parts of the world. Invasive algae like Sargassum and Undaria can out-compete native kelps and alter the entire ecosystem.

Sargassum horneri occurrence - southern California

A map showing the expansion of the non-native seaweed Sargassum horneri in the Southern California Bight from 2003 to 2015. Figure credit: Modified from Marks et al. 2015.

A map showing the expansion of the non-native seaweed Sargassum horneri in the Southern California Bight from 2003 to 2015. Figure credit: Modified from Marks et al. 2015.

Click for Details First seen in Long Beach Harbor in 2003, Sargassum horneri had spread to many mainland and island sites in southern California by 2015. First observed in Channel Islands National Marine Sanctuary at Anacapa in 2009, it had expanded to both Santa Barbara and Santa Cruz islands by 2015. Red ovals highlight observations that are inside Channel Islands National Marine Sanctuary. For more information, consult Figure App.F.14.2 in the CINMS 2016 Condition Report.

Sargassum horneri occurrence - CINMS

Click for Details Locations where the invasive alga Sargassum horneri has been observed in the Southern California Bight. The color of circles denote the year Sargassum was first seen while black circles indicate sites where it has not been observed. Note: This is a more detailed variant of a map that was shown during the expert workshop. For more information, consult Figure App.F.14.3 in the CINMS 2016 Condition Report.

Sargassum horneri percent cover by island

A figure showing the average amount of a species of non-native seaweed (Sargassum horneri) across three of the Nothern Channel Islands from 2010 to 2015. Figure credit: Channel Islands National Park.

A figure showing the average amount of a species of non-native seaweed (Sargassum horneri) across three of the Nothern Channel Islands from 2010 to 2015. Figure credit: Channel Islands National Park.

Click for Details Mean (+/- SE) percent cover of Sargassum horneri at sites monitored by Channel Islands National Park at Santa Cruz (green), Anacapa (blue), and Santa Barbara (red) islands. Cover has recently increased at all three islands. For more information, consult Figure App.F.14.4 in the CINMS 2016 Condition Report.

Watersipora occurrence - Southern California Bight

A map showing the presence (red) and absence (green) of a non-native encrusting invertebrate on oil platforms in the Santa Barbara Channel and around the Northern Channel Islands. Figure credit: Page et al. 2016.

A map showing the presence (red) and absence (green) of a non-native encrusting invertebrate on oil platforms in the Santa Barbara Channel and around the Northern Channel Islands. Figure credit: Page et al. 2016.

Click for Details Presence (red) and absence (green) of Watersipora spp. on recently surveyed oil platforms, other artificial surfaces, and natural reefs in the Santa Barbara Channel. This non-indigenous bryozoan was found to occur on only two of 15 natural reefs surveyed in the northern Channel Islands. For more information, consult Figure App.F.14.5 in the CINMS 2016 Condition Report.